Problem with IPhone 14 pro

Hi,  I had a strange problem with my iPhone 14 pro today, the phone was bought in February 2023. And is under warranty. The phone firmware is 16.4.1 (a). I put the phone on charge yesterday before going to bed when the battery was at 35% charge. In the morning I found that the phone turned off and would not turn on again. I thought it was a charging problem. I tried charging the phone, but even after 30 minutes with charging it wouldn't turn on. Eventually I found a way to reset it. A hard reset helped when I successively pressed the volume and shutdown buttons. I would like to know is it a firmware problem or is there a problem with the phone itself and has anyone experienced this?